Light valves have been in use for more than sixty years for the modulation of light. As used herein, a light valve is defined as a cell formed of two walls that are spaced apart by a small distance, at least one wall being transparent, the walls having electrodes thereon, usually in the form of transparent, electrically conductive coatings. The cell contains a light-modulating element (sometimes herein referred to as an “activatable material”), which may be either a liquid suspension of particles, or a plastic film in which droplets of a liquid suspension of particles are distributed.
The liquid suspension (sometimes herein referred to as “a liquid light valve suspension” or “a light valve suspension”) comprises small, anisotropically shaped particles suspended in a liquid suspending medium. In the absence of an applied electrical field, the particles in the liquid suspension assume random positions due to Brownian movement, and hence a beam of light passing into the cell is reflected, transmitted or absorbed, depending upon the cell structure, the nature and concentration of the particles, and the energy content of the light. The light valve is thus relatively dark in the OFF state. However, when an electric field is applied through the liquid light valve suspension in the light valve, the particles become aligned and for many suspensions most of the light can pass through the cell. The light valve is thus relatively transparent in the ON state. Light valves of the type described herein are also known as “suspended particle devices” or “SPDs.” More generally, the term suspended particle device, as used herein, refers to any device in which suspended particles align to allow light to pass through the device when an electric field is applied. Light valves have been proposed for use in numerous applications including windows, skylights, and sunroofs, to control the amount of light passing therethrough or reflected therefrom as the case may be. As used herein the term “light” generally refers to visible electromagnetic radiation, but where applicable, “light” can also comprise other types of electromagnetic radiation such as, but not limited to, infrared radiation and ultraviolet radiation.
The SPD is laminated between two pieces of glass or plastic to form a sandwich which is sometimes called SPD Glass or SPD Plastic, and which can be further used to form a glass or plastic window. With such SPDs forming a window, the amount of light passing through the window can be finely controlled based upon the characteristics of the electricity passing through the SPD. The degree to which something reduces the passage of electromagnetic radiation is known as opacity. When referring to windows, changes in opacity is often noted as a change in a windows tinting, its light transparency or transparency and each of these terms may be equally be used to mean the same.
Such SPDs are now being installed into glass so that the amount of light passing through the glass can be finely controlled based upon the characteristics of the electricity passing through the glass. At least one method by which such glass and thus its opacity or light transparency may be controlled is described by Malvino, in U.S. Pat. Nos. 6,897,997 and 6,804,040 collectively referred to as the Malvino patents. But a device envisioned by Malvino, while suitable for the manual control of a small number of co-located windows, is not scalable nor does it provide the automated intelligence to actively and dynamically control environments of more than a few windows such as in an automobile, marine vehicle, train or aircraft, to as much as a residential or commercial building or a skyscraper of such SPD windows.
The Malvino patents provide the basis for driving SPD glass by varying voltage at a fixed frequency which will cause the glass to lighten toward clear or to darken so as to block most light passing through it. That device is capable of mapping the non-linear characteristics of SPD into a linear range of values that could be thought of as setting the glass from say 0 to 100%. The range is broken down into a small discrete set of settings for perhaps 6 different opaqueness levels and 6 specific resistor and capacitor combinations are built into the implementation and are manually selected to set the proper voltage for the associated degree of tinting. Through that implementation, a linear manual control, such as a slide switch or a rotating dial may be attached to the Malvino controller to directly vary the amount of light allowed through the glass at any time.
The Malvino patents review the use of a few fixed frequencies at which to drive an SPD. As described, driving the device at a lower frequency tends to have a slight lower energy utilization curve with regard to the power needed to drive the SPD. Frequencies in the range of 15 hertz to 60 hertz were discussed. There is a serious potential problem with the aforementioned controller operating the SPD when driven by these frequencies. It is possible that the SPD will “sing” and be heard as a tone in the B-flat range by being driven by a fixed frequency within that range. An SPD controlled window typically consists of SPD-capable material in the form of a clear Mylar coated with SPD emulation, placed in between two pieces of glass. The SPD is basically sandwiched and held in place by glass on both sides. If 50/60 Hertz current travels through the sandwiched SPD, in some cases, the Mylar will start to vibrate in resonance with the driving frequency and may be heard by people near the window as an annoying hum.
A considerable issue in the wide-scale worldwide deployment of SPD windows, is on how residential and commercial buildings will be wired up to allow some “central intelligence” to operate the individual windows. Today, there is no concept of running wires to windows from some control room in the building. It is not desirable to introduce a new requirement for building wiring in the introduction of SPD glass around the world, since thousands of installation people would need to learn and understand new building wiring requirements. Yet, if any other techniques are employed to “wire” each window to the “central intelligence”, it must require little or no training, and be a relatively low cost so as not to make the use of SPD glass prohibitive.